The invention relates to an improvement in water-proof grommets of synthetic resin used in mounting small parts or the like to a member being mounted, such as body steel-sheet of automobiles.
Water-proof grommets of synthetic resin having a body in the form of a bottomed cylinder for prevention of entrance of rain water or the like are disclosed in Japanese Utility Model Publication No. 22659/1987 filed by the applicant of the present application. FIG. 8 is a cross sectional view showing a water-proof grommet described in the above publication, which grommet is provided with short, upward latch pawls 41 on both sides of an upper portion of a grommet body 40, and a neck 43 below a head 42. A falling-off preventing effect is obtained by inserting the grommet body 40 into a mount hole 31, which is formed in a member being mounted 30, such as body steel-sheet, while flexing the latch pawls 41 inward, and then threading a screw, for example, a tapping screw, into a lumen of the grommet body 40 to expand the grommet body 40 outward to bring the neck 43 into close contact with an inner edge of the mount hole 31 of the member being mounted 30.
With such grommet, however, when the grommet body 40 is intensely pulled upward, tips of the latch pawls 41 abut against a back surface of the member being mounted 30 to exhibit the falling-off preventing effect of the entire grommet body 40 but the tips of the latch pawls 41 are in a free state (engagement is not present between the tips and an underside of the member being mounted) when the grommet body 40 is inserted into the mount hole 31 or when a screw is threaded into the lumen of the grommet body 40. Accordingly, the entire grommet is made axially movable depending upon a thickness of the member being mounted 30. Also, there is involved a problem that since the latch pawls 41 are short, a force (hereinafter referred to as insertion load) required for insertion of the grommet body 40 into the mount hole 31 is great and so the insertion is not easy.
The invention has been contrived to solve the above-mentioned problems of the prior grommets and to provide a water-proof grommet in which insertion load can be reduced further than those of the prior grommets and which prevents the possibility that the entire grommet will be moved axially irrespective of the thickness of a member being mounted.
The water-proof grommet according to the invention comprises a head provided with an insertion hole, and a grommet body provided below the head to be capable of expanding outward as a screw adapted to be threaded into a central hole contiguous to the insertion hole advances. The water-proof grommet also includes at least two latch pawls which are connected at lower ends thereof to the grommet body and which are arranged on an outside surface of a substantially central portion of the grommet body in a longitudinal direction. At least portions of inside surfaces of tip ends of the latch members are adapted to be pushed by the outside surface of the grommet body when the grommet body expands outward, and inclined surfaces formed on upper surfaces of the tip ends of the latch pawls are inclined outward and downward. The inclined surfaces push a member being mounted in an upward direction and an upper surface of the member being mounted is brought into close contact with a flat back surface of the head when the latch pawls are pushed outward due to expansion of the grommet body.
In addition, the inclined surfaces can assume various configurations, for example, generally straight, stepped, steps formed at lower portions thereof, and generally curved.
With the water-proof grommet according to the invention, since upper surfaces of tip ends of the latch pawls include inclined surfaces inclined outward and downward, portions of the inclined surfaces always contact with and push a member being mounted whenever a screw is threaded into a lumen of the grommet body, even if the member being mounted is different in thickness. Therefore, irrespective of thickness of the member being mounted, there is no possibility that the entire grommet can move axially. Also, since lower ends of the latch pawls are connected to a substantially central portion of the grommet body, adequate elasticity is ensured for the latch pawls with the result that load at which the grommet body is inserted into the member being mounted can be reduced further than with the prior grommets.